Directed, heritable alterations in gene expression, called epigenetic changes, are involved in stabilizing cell differentiation. Our working hypothesis is the tumor transformation in higher plants, and perhaps generally, is due to reversible epigenetic changes rather than permanent changes in the host cell genome. We have developed one of the very few experimental systems in which epigenetic changes affecting tumor autonomy can be induced and reversed at will. It is our intention to characterize further such changes and begin to look for molecular mechanisms using cultured crown-gall and normal cells of tobacco.